Study on return voltage measurement of oil-paper insulation testing technology in transformers

Transformer is one of the most important equipment in the power system, assuming the voltage conversion, distribution, transmission of electrical energy mandate in power network, which is an important prerequisite for safe and stable operation of power system. Once the transformer fault, it may lead to blackouts, and even the collapse of the power network, causing huge economic losses. From the point of view of economy and safety, it is necessary to carry out insulation diagnosis and life assessment for prolonging the service life of power transformer. Dielectric response measurements are a technology that is used to detect the insulation condition of transforms. In recent years, a series of non-destructive test methods based on the dielectric response theory of transformer have been developed, including frequency domain dielectric spectroscopy (FDS) in the frequency domain and the polarization and depolarization current (PDC), the return voltage method (RVM) in time domain. On the basis of dielectric response technology, this paper discusses the time domain dielectric spectroscopy of PDC and RVM, also including the conversion algorithm between the two methods. The RVM method has the advantage of adjusting the discharge resistance of the external circuit, which can calculate the equivalent parameters of dielectric, and the PDC takes into account the characteristics of the oil, the conductivity of the oil, the insulation structure and material properties and so on. The physical basis of the RVM and PDC methods is similar, but the use of the RVM method for testing is more complex than the PDC method. So it is necessary to study the conversion algorithm from PDC to RVM, which improve the flexibility of time domain dielectric spectrum test. The derivation and experimental verification of the algorithm are presented in this paper.